1. Field of the Invention
The present invention relates to a display device, especially to that having a light emitting element. The invention also relates to electronic appliances including the display device having the light emitting element.
2. Description of the Related Art
Recently, mobile phones have been used widely with the advance in communication technology. It is anticipated that moving images and much more information will be transmitted using mobile phones in future. Meanwhile, personal computers (PCs) that are portable have been produced, owing to reduction in weight thereof. A large number of personal digital assistants referred to as PDAs have been produced beginning from an electronic organizer so that they are in course of being popularized. Further, a flat panel display is mounted on most of the portable information appliances, owing to the development of the display device.
Furthermore, recently, commercialization of the display device using a thin film transistor using low-temperature polysilicon (hereinafter, a thin film transistor is referred to as a TFT) has been proceeded among active matrix display devices. In case of using the low-temperature polysilicon TFT, it is possible that a signal line driver circuit is formed on the periphery of a pixel portion over the same substrate as the pixel portion; therefore, the display device can be downsized and defined highly and it is expected to be used more widely.
In case of a mobile phone, a folding type one has been taking the place of a bar type one. Such a folding type mobile phone is shown in FIG. 2A, which includes a first housing 201, a second housing 202, a display portion 203, a speaker 204, an antenna 205, a hinge 206, an operating key 207 and a microphone 208 (see Japanese Patent Laid-Open No. 2001-326710, for example).
In case of the mobile phone using a conventional light emitting element, there was a problem that images could not be seen because, under strong outside light such as sunlight, the outside light was stronger than light emitted from the light emitting element. As shown in FIG. 2B, color of display on the display screen seems almost black by strong outside light when seen by a user. In case of a display device using a liquid crystal, this problem is solved by utilizing a reflective liquid crystal display device. However, it was a problem that a basically similar solution can not be applied to the display device using the light emitting element.